Question

请随意创建一个Windows窗体应用程序。要重现错误，请禁用网络连接并运行代码。它会在每1秒后尝试重新连接。在4-5次尝试启用网络连接后，在调试模式下，您会注意到即使提取产品，也会调用Reconnect（）方法4-5次。获取产品后，为什么一次又一次地调用Reconnect（）方法？

        string apiUrl = "https://api.gdax.com/products";
        string json;

        private void Form1_Load(object sender, EventArgs e)
        {            
            try
            {                
                if (FillProducts()) // product need first
                {
                }
            }
            catch (WebException ex)
            {
                ReconnectOnError(ex);
            }
        }
        private bool FillProducts()
        {
            bool isDone = false;
            try
            {
                json = GetGDXJSONData(apiUrl);
                JsonSerializer serializer = new JsonSerializer();
                DataTable dt = (System.Data.DataTable)Newtonsoft.Json.JsonConvert.DeserializeObject(json, (typeof(System.Data.DataTable)));

                count = dt.Rows.Count;

                if (count > 0)
                    isDone = true;
            }
            catch (Exception ex)
            {               
                isDone = false;
                ReconnectOnError(ex);
            }
            return isDone;
        }

        int count = 0;
        private void ReconnectOnError(Exception errorMessage)
        {
            try
            {
                Thread.Sleep(1000);
                if (count < 1)
                {
                    FillProducts();     // it comes on this point again and again even the count is greater than 1
                    Reconnect();
                }
                else
                {
                    Reconnect();
                }
            }
            catch (WebException ex)
            {
                ReconnectOnError(ex);
            }
        }

        private void Reconnect()
        {
            // why this is called the number of times the attempt was made to fill the products?
        }      

        private string GetGDXJSONData(string apiUrl)
        {
            HttpWebRequest request = (HttpWebRequest)WebRequest.Create(apiUrl);

            request.Method = "GET";
            request.ContentType = "application/json";
            request.UserAgent = "gdax-node-client";
            request.Accept = "application/json";

            HttpWebResponse response = (HttpWebResponse)request.GetResponse();
            string responseString = new StreamReader(response.GetResponseStream()).ReadToEnd();

            return responseString;
        }
    }

编辑 - 这是一个示例代码，一旦获取产品，我在Reconnect（）方法中做了很多事情。此外，如果在获取产品后发生错误，则不要获取产品，只需调用Reconnect（）方法，这就是其他原因。

Edit2 - 请不要仅仅通过查看代码来回复。如果您已经创建了一个表单并自己运行并且可以自己查看错误，那么请告知如何解决此问题。

更新 - 我知道我进入了无限次迭代。我试过这个，现在它起作用了：

    string apiUrl = "https://api.gdax.com/products";
    string json;

    private void Form1_Load(object sender, EventArgs e)
    {
        if (FillProducts()) // product need first
        {
        }
    }

    bool isOk = false;
    private string GetGDAXProducts()
    {
        try
        {
            json = GetGDXJSONData(apiUrl);
            return json;
        }
        catch (Exception ex)
        {               
            return "-1";
        }
    }

    int count = 0;
    private bool FillProducts()
    {
        bool isDone = false;
        string retVal = GetGDAXProducts();

        while (retVal == "-1")
        {
            retVal = GetGDAXProducts();
        }

        if (retVal != "-1")
        {
            JsonSerializer serializer = new JsonSerializer();
            DataTable dt = (System.Data.DataTable)Newtonsoft.Json.JsonConvert.DeserializeObject(json, (typeof(System.Data.DataTable)));

            count = dt.Rows.Count;

            if (count > 0)
                isDone = true;
        }

        return isDone;
    }

    private string GetGDXJSONData(string apiUrl)
    {
        HttpWebRequest request = (HttpWebRequest)WebRequest.Create(apiUrl);

        request.Method = "GET";
        request.ContentType = "application/json";
        request.UserAgent = "gdax-node-client";
        request.Accept = "application/json";

        HttpWebResponse response = (HttpWebResponse)request.GetResponse();
        string responseString = new StreamReader(response.GetResponseStream()).ReadToEnd();

        return responseString;
    }

Answer 1

这是因为如果没有网络连接，那么调用API网址无法连接，并且在catch阻止您尝试重新连接

        catch (Exception ex)
        {               
            isDone = false;
            ReconnectOnError(ex);
        }

Answer 2

你在这里有一个无意的循环：

如果FillProducts失败，它会自行调用......

迭代：FP失败
迭代：FP调用ReconnectOnEx调用FP，再次失败
迭代：FP调用ReconnectOnEx调用FP调用ReconnectOnEx ...

并返回

现在整个堆栈将在每次调用Reconnect时展开。

private bool FillProducts()
    {
        bool isDone = false;
        try
        {
            /* ... Fails if no connection ... */
        }
        catch (Exception ex)
        {               
            isDone = false;
            ReconnectOnError(ex); // ==> BLOCKS !!
        }
        return isDone;
    }

    int count = 0;
    private void ReconnectOnError(Exception errorMessage)
    {
        try
        {
            Thread.Sleep(1000);
            if (count < 1)
            {
                FillProducts();     // <== Will result in another call to this method. Returns on 1st Succeeding call to FillProducts.
                Reconnect();        // <== Will be called as soon as FillProducts returns.
            }
            else
            {
                Reconnect();
            }
        }
        catch (WebException ex)
        {
            ReconnectOnError(ex);
        }
    }

为避免这种情况，您可以将“重试”逻辑移动到FillProducts方法中：

private bool FillProducts()
    {
        // To prevent waiting forever ...
        int retryCount = 10;

        bool isDone = false;
        while ( !isDone && (retryCount-- > 0) )
        {
            try
            {
                /* ... Fails if no connection ... */

                // OnSuccess=>
                isDone = true; // will break the loop.
            }
            catch (Exception ex) // You should actually catch a more specific Exception here
                                 // ... but that's a different question.
            {               
                isDone = false;
                // Just omit this! >>> ReconnectOnError(ex); // ==> BLOCKS !!
                // If you want, you can add a little delay here ...
                Thread.Sleep(1000);
                // From your code, I guess this has to be called on failure ...
                Reconnect();
            }
        }
        return isDone;
    }

要考虑的其他几点：

您不应该在GUI线程上进行网络I / O.您的GUI可能会无响应。考虑使用async / await（任务异步模式）
捕捉Exception可能不是最好的主意。您应该捕捉到最具体的例外情况，并让其余部分由调用者处理。

Answer 3

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当没有互联网连接时.Count变量始终为零。

Winform递归循环 - 一次又一次地调用方法

3 个答案: